For several decades, there has been an increase in the use of disposable containers by consumers at the workplace, in public areas such as parks, beaches, campgrounds, and the like, as well as in the home. Generally, disposable, nestable containers made of foam materials—e.g., Styrofoam®—and insulated paper were once the only alternatives to glass or reusable plasticware containers. However, in recent years, thermoformed plastic molded containers have been a replacement to the less environmentally concerned foam articles in the industry. In particular, the use of nestable thermoformed containers has been on the rise. These thermoformed articles are also remarkably useful in containing cold fluids.
Thermoplastic materials are particularly advantageous for manufacturers as the materials do not require expensive foaming agents and need no surface lamination—each of which is a feature resulting in fewer stages of the manufacturing process. Moreover, for consumers, containers constructed from these materials are generally more durable than paper containers, are usually of a single-piece construction, and are inexpensive and recyclable.
Thermoforming begins with a thin sheet or web of material such as polyethylene, polypropylene, polyester, or polystyrene having a thickness within a range of from approximately 8 mils to 100 mils, depending on the size of the container to be manufactured. Cups and similar articles are typically made from plastic sheet having a pre-thermoforming thickness from approximately 30 to 60 mils, but the finished articles may be thinner after thermoforming. The sheet or web is heated to a temperature suitable for thermoforming—in a range from approximately 110° C. to about 200° C. for the above-mentioned materials—and is thereafter fed into a conventional forming machine in which the process proceeds under applied positive and/or negative air pressure conditions. A mold cavity is used to impart a particular formational construction into the thin-walled container as the plastic material is drawn into the mold using vacuum pressure on one side of the article and/or a positive pressure on the opposite surface of the material. The formational construction of the container may be decorative, but generally has a particular utility—e.g., texturing for grasping and formations for nestability in addition to other utilities. The processing period for a normal thermoforming operation is typically between 1 and 20 seconds.
One disadvantage to many existing cup and container designs is that the round design is not conducive to gripping, a problem encountered with all cup designs, but especially in larger-volume cups. The user must often exert more than a desirable amount of gripping pressure, in order to stabilize a cup that is too large to wrap fingers around. Additionally, cold drinks often cause condensation on the outside of a cup, creating a problem with slipping, especially with smooth plastic cups. Although this slipping is a problem itself, it can be exacerbated in a cup lacking a stable gripping surface. Annular ribs may increase the friction between the cup and the user's hand to help alleviate slipping, but do not do anything to remedy the gripping problems associated with the round design. Therefore, a need exists to provide a more ergonomic and stable gripping surface for a thermoformed plastic cup, especially a larger-volume cup, while at the same time reducing slipping caused by condensation on the outside of the cup.
Another problem with thermoformed plastic nestable containers is structural integrity. Sidewalls of thin-walled thermoformed containers often bend and deflect inward easily when grasped by a user. A deflection of this sort may constrict the volume of the container causing unpleasant fluid overflows. Additionally, deflection of the sidewall can make the container more difficult to grip, as well as potentially leading to cracking. One solution to the identified problem is to provide thicker material constructions, but this increases production costs. Additionally, thicker constructions tend to increase the stack height among nested containers. These respective phenomena limit the number of containers that may be nested in a confined area and can prevent the nested containers from being easily separated. Another, more effective means known and used in the art is creating annular ribs and/or shoulders in the sidewall, which can add significant rigidity to the surrounding areas of the sidewall. Creating rigidity-enhancing features in the sidewall avoids the problems associated with using a thicker sidewall. However, the strength enhancement that may be achieved by using ribs and shoulders is limited, especially in the middle regions of the sidewall, where gripping normally occurs. Therefore, a need exists to further increase the strength of the sidewall of a thermoformed container, while avoiding the use of thicker material.
The present invention solves these two problems primarily by creating arcuately formed longitudinal recesses in the sidewall. These recesses both provide an ergonomic and effective gripping surface and increase structural integrity. However, the recesses can create problems with proper nesting of the containers, which tend to telescope because of their lack of complete rotational symmetry. Thus, a need further exists for a means to ensure proper nesting of containers having recesses in their sidewalls.
Additionally, containers having recesses in their sidewalls may rub together during manufacturing. Cups are often stacked inside each other while being transported along a line by machinery during certain manufacturing processes. The cups may rotate during this movement, causing them to rub against the cups stacked above and below them. This rubbing can create wear on the cup, scratching the surface. While not all manufacturing processes present this problem, it can be a source of concern when manufacturing containers having recesses in their sidewalls. Thus, a need exists to solve the problem of rubbing caused by movement and rotation of the cups during manufacturing.
The present invention provides an economical solution to the recognized problems. The present invention is intended to provide a suitable formational construction for thin-walled thermoformed containers.